I personally like feeding frozen food (brine shrimp, mysis shrimp, bloodworms, daphnia) and live wingless fruit flies are fun! :D One time a moth landed in one of my bettas tanks and got stuck. I got to witness my betta eat him! It was amazing, I think I held my breath the entire time. xD
It's nice to have lots of plants to swim around, under, over at all different levels, especially ones that leaf out so the bettas can relax on them. Bettas are curious and like to explore (just make sure there's nothing they can get stuck in). When I do my full water changes I like to rearrange their decorations and sometimes add new, it gives them something new to check out. ^^